No prior hedgehog antagonist vismodegib or other antagonists of the hedgehog pathway, and no prior temozolomide treatment for patients to be randomized in Arm A or B. Patients previously treated with temozolomide are eligible for enrollment in study arm C on a case by case basis and following sponsor agreement More than 4 weeks since prior myelosuppressive chemotherapy (6 weeks for nitrosoureas, 6 months after high dose therapy) or immunotherapy At least 3 months since prior craniospinal irradiation (≥ 23 Gy) At least 8 weeks since prior local irradiation to primary tumor At least 2 weeks since prior focal irradiation for symptomatic metastatic sites.